The Viral Epidemiology Branch, National Cancer Institute is initiating a new cohort and nested case-control study of cancers occurring in persons with human immunodeficiency virus (HIV) associated immunosuppression. Five thousand subjects will be recruited from AIDS treatment and clinical trial sites to be followed prospectively for cancer endpoints. Baseline data and blood samples will be collected on cancer cases. One hundred-fifty cases of non-Hodgkin's lymphoma, a similar number of cases of Kaposi's sarcoma, and approximately 45 cases of other cancers are expected over a 3 year follow-up. Data from this study will be used to identify rates and risk factors for HIV-associated malignancies. Therapies for HIV will be specifically investigated as potential risk factors. The biologic specimens will be analyzed for etiologic factors and intermediate markers for HIV-associated carcinogenesis. This study will generate a larger collection of HIV associated tumors linked with pre-cancer sera and lymphocytes than any of the current U.S. natural history cohorts. These materials will increase our ability to characterize HIV associated carcinogenesis and address basic issues regarding neoplasia.